Tuning fork and control system



May 10, l949 A. G. cooLEY 2,469,951

TUNING FORK AND CONTROL SYSTEM :l INVENTOR. /Q//ST//v @wir UM ya? May 10,1949 A. G. cooLEY 2,469,951

TUNING FORK ANDy CONTROL SYSTEM Filed OOC. l0, 1945 5 SheetS-Shee 2 JNVENTOR. fasr//V 6 @00L/SY May 10, 1949. A. G. COOLEY 2,469,951

TUNING FORK AND CONTROL SYSTEM Filed OCL. l0, 1945 3 She'ets-Sheet 5 IN VEN TOR. a//V- G @am y Patented May 10, 1949 vfowl'-rr;o STATES PATENT .ortica "f 'TUNINGFOEIi INTROIFSYSTEM n Austin G.- Cooley, New-York, N. .Yf.,assignery to Times Facsimile Corporation, a'I-corporatioriof New York i *Application October 10; 41945;"Sel'tll-Noi621,410?,

21. Claims. (01.84%457) This invention'relates to ffrequency` control aprparatus andfmore especially ytorimprove'd tuning 4fork constructions.

A principalobject is to provide animproved tuning fork ".unitnwhich" has a Vhigh 'degree of 1 frequencyistability ascompared with prior-.known i v lconstructions.

f 'Anotherobject-'is to provide a tuning fork which is enclosed` Within. al sealed. container, together With1means 'iorffmechanically adjusting the f'naturalirequencyofathe -fork'externally of the fr container.

Afffeature of the invention relates to novel ar- .1 rangements foriadjusting.. the i natural` vibrating "Pfrequency of atuningtfork or the like.

f lAnother.featurerelates to-animproved-tuning -iorkfunit havingth'e fork Vtinesllmounted Within ian evacuatedlen'closure or-vvthin a' gas-filled renc'losure.

A 'further vfeature relates'to a-frequency control system of the typehernploy'ing avtuning fork associateclfwith electron tube circuits, the tuning yfork 'being mounted *and -adjusted 'so that the Ifrequencystability of thesystem isdetermined to avery highlde'gree by the natural vibrations of the fork itself. n

A still further "fe'ature'frelates to thenovel a highly stable tuningfork Vcontrol system.

Y Other 'features'and-advantages not specically enumerated' will be apparent after a consideration ofthe following vdetailed description and the .of the invention.

In V.controlled "frequencysystems of the kind employing tuningrforksas a primary frequency control element, it isi-.desirable to have the fork oscillate at its ownnatural period, rather than to force. theiork to vibrate at a spe'cied. fre- .quency eitherby" damping crever-driving by electrical"excitation. `In" systems where the fork isv freelyvibrating as vdistinguished' from forced or damped vibration-,fthe frequency stability is much'- greate'xibecause the Leffectfof `variations in theassoci'ated electricalfcircuits is very small.` On the other hand.;whereftheaiorkis over-driven or damped thef associatedelectrical circuits are not 'entirely stable-because of-'thetendency of-'the various-*circuits components* such as .P Ltubes,

. capacitors; resistors 'and' the lliketo -change either 2 as a-.result ofxageY or:.as `af-result of: temperature or. humidity` conditions.-Thesezchanges result in corresponding `frequency instability; The-desired objectsl according to the: present invention? are achieved by:` mountingxtheforkttines in a'hermetically sealed.:.container :and by'ff'locatin'gthe i: driving; :andi `pick-up lcoil's' or` magnets outside of fthe Y."container: Preferably, Hthefcontainer is evacuated, .although ifadesire'd a"s'electedI gas may -i be `supplied'.frinsid'e thefichaimber under@l suitable DIYGSASUTB.

r'FJ/hile itha'sfb'een proposed heretofore to mount v a" complete.: tuning .-forkiunitl including its coils Within arievacuatedlire'ceptacle; suchdeviceshave Wherefthenentire! unitdincludin'g" the'v tuning 'fork lorganization'. arrangement vand relative interl connection of parts which' cooperate to provide "andi other similari partis!l located-"-Withinlthe receptaclegsparticularly: 'since'lsuchcoils' usually? 'con- Y tain impregnating materials"landcoatingIn-aterials suchas tvarnishf o'r 'f theilike.- l" Furthermore,

with such arrangements, it isf necessary to-lbring Tout -the electrical connectionsithrough'thelwall of the re'ceptaclefand these"` connections must be i sealed through the vvallvk in a vacuum-tig'l'itv imaninein!:Theirnultiplicity'of s'uch'fconnections may llead tof-leaks?" The `Iproblem isfurthercomplicated by the lfact :that the frequency of 4the fork' when lin a vacuum' is different fror'nit's frequencyfwhen theiorkr is at atmospheric pressure?. 1'Consequently, it become'srnecessary'toprovide-means vto be `able toadjust thefnatural frequency fithe fork :even 1 after it is v"enclosed -within @the evacuated or gas-lined" container.

` -One f arrangement1` for 'overcoming` Ithev `v`disadvantages of the'prior arrangements is? illustrated Vin'Fig;'ll'ftlfle drawing;I Whereinthetuninglfork isA mounted 'with' its vtines 2s and '3 located within a "suitable container' or housing 4'. The; housing 4 where the Lfork =l"pa'sse'stherethrough is `sealed of a vheader 52 itbeing.understoodlthattheljoint betweenl'th'e'header 5 andthe-'fork l' is-Hhermeti- 'i cally sealed orf'vacuum-tighttsealedl-in-'anylwell- 1 knownlfmannenfviorexample asfshownl in' U. S.

,. the same numerals.

Patent No. 1,093,997. The inside dimensions of housing 4 are chosen so as to provide sufficient space for the vibrations of the fork tines, and of course the housing 4 should preferably be constituted of a non-magnetic material.

Suitably mounted exteriorly of the housing l adjacent the lower end of the fork tines are a driving electromagnet 5, and a pick-up electromagnet 'i'. Magnet E may be energized from any suitable source of pulsating or alternating current of a frequency equal to or closely adjacent to the natural frequency of vibration of the fork I. If desired, the electromagnet coil 6 may form part of a conventional electron tube oscillator feedback circuit. Since it is not always possible to estimate with the desired accuracy the amount of change in natural frequency which the fork will exhibit when mounted in a vacuum as compared with its natural frequency at atmospheric pressure, it is necessary to provide means for adjusting the natural frequency of the fork after it is sealed through the receptacle 4. It will be understood of course that the fork is sealed in, to a point beyond the heel portion 8 so that the entire length of the tines is within the housing Heretofore, it has been the usual practice to adjust the frequency of the system as a whole by changing the electromagnetic driving force on the fork tines or by changing the electromagnetic load on the fork tines. However, since it is desirable to have the driving load as small as possible for the sake of frequency stability, it is not possible to achieve much in the way of frequency adjustment by the usual driving or magnetic loading of the electrical controls. However, in order to achieve the necessary adjustment of the frequency of the system while maintaining the fork freely vibrating at its natural period, the yoke portion is provided with b-ores Il] and ll, which extend part way into the body of the respective tines 2 and 3. The internal surfaces of each of the bores lil and II are threaded to receive corresponding threaded plugs I2, I3. Each of the plugs is provided on its upper face with a slot vI4 to enable it to be turned so as to vary its vposition interiorly of its respective bore. Preferably also, the lower face of each of the plugs is slotted atv I3a, Ilia so that the lower end of each plug is slightly sprung outwardly to provide a relatively tight and resilient pressure between the plug and the bore at its lower end. This results in giving the plug a lock-nut effect. It will be understood of course, that any vother wellknown means may be provided for locking the plugs I2 and I3 in their adjusted positions within their respective bores. By adjusting one or both of the plugs I2 and I3, the natural vibrating frequency of the tuning fork can be adjusted to the desired frequency `of the system to be controlled. Under these circumstances, the fork acts as the primary frequency control member and the frequency of the system is determined by the natural vi-bratory frequency of the fork tines.

Referring to Figs. 3 and 4, there is shown a modified arrangement for effecting frequency adjustment of the fork, and parts of Fig. 3 which correspond to those of Fig. 1 are designated by In this embodiment, the bores I5a and Illia instead of being internally threaded, have two rods I5, I6, fastened at their lower ends within the lower ends of each yof the bores. For this purpose, the lower end of each bore may be tapered at |5b and IEb and the rods I 5, le, may likewise have their lower ends tapered at I5c, Ic so as to provide a drive iit beand the fork tines. As shown in Fig. 3, the rods I5 and I6 are of smaller diameter than their corresponding bores so as to allow the rods to lbe drawn together or spread apart at their upper ends. For this purpose, the upper ends of the rods I5 and I6 are provided each with a threaded opening I5d, I'Gd to receive the ends of a threaded arm I'l to which is rigidly attached an adjusting thumb nut I8. The threads on the ends of member I1 and the threads in the rods I5 and I'S are so arranged that by turning the nut I 3 in one direction, the rods i5 and Iii are drawn closer together, and when nut I 8 is turned in the opposite direction the said rods are spread apart. By this means a closely adjustable stress can be placed on the rods I5 and IS, and this stress will be transferred to the tines 2 and 3 to affect correspondingly the natural frequency of vibration.

Figs. 5 and 6 represent a modification of Fig. 3, and the parts which are similar in both figures bear the same designation numerals. In this embodiment, the rods I5, I6, and the corresponding bores are omitted. However, the yoke 9 is provided with two external arms I9, 2li, which may be considered as integral extensions of the fork tines 2, 2. The arms I9 and 2G have threaded openings ISa, 23a to receive the right and lefthand threaded end sections of the adjusting rod I l which carries thumb nutl I8. Therefore, by turning the nut I8, the natural period of vibration of the fork tines 2, can be very closely and accurately regulated. If desired, the rods i5 and IE in the embodiment of Fig. 3 may be chosen of some suitable met-a1 so that any change in frequency of the fork tines which tends to result from temperature changes is compensated for by a corresponding but opposite change in .the rods I5 and I5. To a certain extent, this automatic temperature compensation is inherent in the construction of Fig. 5. Thus, change in temperature which tends to increase the natural frequency vibration of the fork tines changes the stress on the arms I9 and 20 in such a way as to tend to lower the natural frequency of vibration of the fork an equal amount.

Referring to Fig. 7, there is shown a further modification wherein the tuning fork I is enclosed within a cylindrical metal tube 2l which is of seamless and stainless steel tubing which however is substantially non-magnetic and has a comparatively high electrical resistance. An example of such steel that may be used is that sold under the trade designation Stainless Type 304 manufactured by Allegheny Ludlum Steel Corporation. The member 2I at its lower end has its wall thickness considerably reduced so as to enable the drive electromagnet 22 and the pick-up electromagnet 23 to be positioned as close as possible to the fork tines 2, 3. The lower end of member 2I is vacuum-tight sealed by means of a metal cap 2 which is brazed or solder-sealed to the lip of tube 2l. Likewise, the upper end of the fork I is brazed or solder-sealed around its periphery to the corresponding wall of the member 2 I. For the purpose of adjusting the frequency of the fork, the lower end of each of the bores 25, 26, is threaded to receive an adjusting bolt or screw 21, 23. Each of the adjusting screws is provided with a coiled compression spring 29, 39, one end of which abuts against the end of the nut and the other end of which abuts against the corresponding screw head 3|, 32. It has been found that by turning the screws 2'I and 28, a precise adjustment of the natural tween the rods 4 also been found that for a tflnal.A adjustmentxif required, the magnets 22 andi23maytbeadjusted :along the length ofthe fork tines aslight Aamount as .indicated by the"full-lineiarrows. "`When'the `magnetshave beenproperly adjusted, they may be lvfastened 'in position rbyimeans Vof; suitable clamps (not shown) which connect the heel ,por-

"tions 134, to a suitable l'rigid iframe (not shown) llnst'ead of.: sliding' the. magnets? 22 and further the vacuum-tight sealing of the fork unit, 15

comprising members 2| andY 2,4, this unit may be dipped in vacuum sealing varnish of any Wellknown l :ind,such` for-.example asthat sold under the trade name Apiezon-W manufactured Vbyff'echnical Products, Ltd.,fLondon, England. AA further precaution. against leakage may be p-rovided by exteriorly tinning the fork unit.

It will-be understood that thedimensional configurations shown in the embodiments of Figs. 1

to 6 are merely representative and preferably the kdimensions for the various units should be as indicated in the embodiment of Fig. 7.

While certain specic embodiments have been disclosed herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A frequency control d-evice comprising an evacuated housing, a tuned vibratory member hermetically sealed through a Wall of said housing with a portion thereof interior of the housing and with a portion exterior of the housing, a passage-way in said member but accessible from the exterior of said housing, and an adjusting member in said passage-Way and accessible from the exterior of said housing for mechanically adjusting the natural frequency of said vibratory member.

2. A frequency control device comprising a tuning fork, a gas-tight housing within which the tines of the fork are hermetically sealed, said fork having a portion external of the housing, and means mechanically attached to said external portion of the fork for mechanically adjusting the natural frequency of said tines Without affecting said seal.

3. A frequency control device comprising a tuning fork, a gas-tight housing within which the tines of the fork are hermetically sealed, a passage-Way into at least one of the tines which passage-Way is external to said housing, and a member in said passage-Way and accessible externally of said housing to adjust mechanically the natural frequency of vibration of the fork.

4. A frequency control device according to claim 3 in which said passage-Way is internally threaded and a corresponding threaded plug is adjustably located therein.

5. A frequency control device comprising an evacuated housing, a tuning fork a portion of which is sealed in a vacuum-tight manner through a Wall of said housing and with the fork tines located within the housing, a passage-Way in the body of each fork tine, and external to said housing and accessible from the exterior of the housing, and a member in each of said passage-ways for mechanically adjusting the natural frequency of the fork.

6. A frequency control device according to fclaim-5 Ain which `each of the last-mentioned members comprises aplugwhich is adjustable lengthwise Within the Acorresponding passage- Way.

TLAtuning forlchavingia pair of bores each "communicating with the interior vof a fork tine, Iand an adjustable plug frictionally held Within .each of said'bores for mechanically adjusting the natural.frequencyofv vibration of the fork.

18.'.-Atuning fork having a pair of spaced extensions integrally united with the fork tines and :extending from the heel of the fork in a direction opposite to that of the tines, and adjustable means; connectingsaid extensions for subjecting saidextensions to an adjustable stress and thereby to control mechanically the natural frequency Iof vibration of the fork.

L 9. A tuning fork accordingto claim 8 in which i said .-.extensions have' opposit'ely threaded openings .to receive a `bar having corresponding op- 'positely threaded end portions, and means to "turn said bar to control the stress on said extensions .10. `A tuning fork unit comprising an evacuated enclosing J receptacle .having a portion of its peripheral wall thinner than the remaining portion, electromagnetic fork control means mounted externally of said receptacle adjacent said thin Wall portion, a tuning fork mounted Within said receptacle and with the tine ends located adjacent said thin Wall portion of the receptacle, the heel of the tuning fork being sealed in a vacuum-tight manner through a Wall of said receptacle.

11. A tuning fori; unit according to claim 10 in which said receptacle is of seamless metal tubing With the heel of the forli hermetically sealed through one end of the tubing and the other end of the tubing is hermetically sealed by a metal cap.

12. A tuning fork unit according to claim 10 in which the fork is provided with two bores which are accessible exteriorly of the unit each bore having a threaded rod therein and a compression spring between the external end of each rod and the end of the unit.

13. A tuning fork unit comprising an evacuated enclosing receptacle having a portion of the Wall thereof constituted of a material which is substantially non-magnetic, said portion of the Wall being of thinner cross-section than the remainder of the Wall, a tuning fo-rk Within said receptacle and having its heel portion sealed through another part of the receptacle Wall so that the fork tines are adjacent said thinned wall portion, and electromagnetic fork control means located exteriorly of said thinned Wall portion and adjustable with respect to the tines to control the operating frequency of the fork.

14. A tuning fork unit according to claim 13 in which said thinned Wall portion is of stainless steel.

15. A tuning fork unit according to claim 13 in which said receptacle is of stainless steel one end of which is sealed by a metal cap, the said heel portion of the fork being sealed through the opposite end of said receptacle and with the fork tines in close proximity internally with respect to said thinned wall portion.

16. A frequency control device, comprising a tuned vibratory member, a hermetically sealed housing, said tuned member having a portion of its length located within said housing and a portion external to said housing, and means adjustably connected to said external portion for adjusting the natural frequency of said member Without aiecting the said seal.

17. A frequency control device, comprising an evacuated housing, a tuned vibratory member having a portion hermetically sealed through a Wall of said housing and having the greater part of its length within the housing and a portion external to the housing, and means adjustably attached to said external portion for mechanically adjusting the natural frequency of vibration of said member.

18. A tuning fork having a tine thereof with at least one part of its length hollow, and means movable in said hollow portion forv mechanically adjusting the natural frequency of vibration of the fork.

19. A tuning fork unit, comprising an evacuated enclosing reeeptacle for the fork and having at least a portion of the receptacle wall constituted of a material which is substantially nonmagnetic, a tuning fork having its heel portion attached to one end of said receptacle, the tines of the fork extending interiorly of the receptacle to a point adjacent said wall portion, and electromagnetic means located exteriorly of said Wall portion in magnetic alignment with the end portions of the tines for controlling the operating frequency of the fork.

20. A tuning fork unit according to claim 19 in which the said heel portion is integrally united with one end of said receptacle, the other end of said receptacle being hermetically closed by a cap.

21. A tuning fork unit according to claim 19 in which said receptacle is in the form of a stainless steel tube.

AUSTIN G. COOLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,257,684 Dixon Feb. 26, 1918 1,466,623 Houghtaling Aug. 28, 1923 1,958,071 Schofield May 8, 1934 2,034,282 Buckingham Mar. 17, 1936 

